The present disclosure relates to a magnetic coupling element that magnetically couples with another magnetic coupling element or foreign matter, and to an apparatus (magnetic coupling apparatus) and system (magnetic coupling system) utilizing such a magnetic coupling element.
More particularly, the present disclosure relates to a detecting apparatus, a power receiving apparatus, a power transmitting apparatus, and a contactless power supply system configured to detect the presence of foreign matter (such as metal, a magnetized body, or magnet) which may generate heat due to magnetic flux between a contactless power supplying apparatus and an electronic device constituting a contactless power supply system.
Recently, increasing attention is being given to power supply systems that supply power (transfer power) to a consumer electronics (CE) device, such as a mobile phone or portable music player, for example, in a contactless manner (referred to as contactless power supply systems or contactless power transfer systems, for example). With such systems, charging is initiated not by inserting (connecting) the connector of an AC adapter or other power supply apparatus into a CE device, but rather by simply placing an electronic device (the secondary device) onto a charging tray (the primary device). In other words, a terminal connection between the electronic device and the charging tray is unnecessary.
Electromagnetic induction is established as a technique for supplying power in a contactless manner as above. Meanwhile, contactless power supply systems using a technique called magnetic resonance which utilizes the resonance phenomenon have been gaining attention recently.
Contactless power supply systems using magnetic resonance are advantageous in that the principle of the resonance phenomenon may be utilized to transfer power between devices separated by greater distances than those of electromagnetic induction. Additionally, there is an advantage in that the transfer efficiency (power supply efficiency) does not fall significantly even if the axis alignment between the power source (transmitter coil) and power recipient (receiver coil) is somewhat poor. However, magnetic resonance-based systems and electromagnetic induction-based systems are alike in that both are contactless power supply systems (magnetic coupling systems) utilizing a power source (transmitter coil; a magnetic coupling element) and a power recipient (receiver coil; a magnetic coupling element).
Meanwhile, one important element in contactless power supply systems is the thermal regulation of foreign matter, such as metals, magnetized bodies, and magnets, which may generate heat due to magnetic flux. If foreign matter becomes interposed in the gap between the transmitter coil and the receiver coil when supplying power in a contactless manner, there is a risk of causing the foreign matter to generate heat due to the magnetic flux passing through that foreign matter. This risk is not limited to electromagnetic induction-based or magnetic resonance-based systems. Such heat generation in foreign matter may lead to currents being produced in a foreign metal due to the magnetic flux passing through the foreign metal (eddy currents, current loops, circular currents), or to hysteresis loss being produced in a foreign magnetized body or foreign magnet due to the magnetic flux passing through the foreign magnetized body or foreign magnet.
A large number of techniques that detect foreign metal by adding a foreign matter detection system to a contactless power supply system have been proposed for such thermal regulation. For example, techniques using an optical sensor or a temperature sensor have been proposed. However, detection methods that use sensors may be costly in the case of a broad power supply range, as with magnetic resonance-based systems. Moreover, use of a temperature sensor, for example, may impose additional design constraints on the transmitting and receiving devices, since the output results from the temperature sensor will depend on its surrounding thermal conductivity.
Thus, there have been proposed techniques that determine the presence of foreign metal by looking at changes in parameters (such as current and voltage) when a foreign metal comes between the transmitter and receiver. With such techniques, it is possible to curtail costs without imposing design or other constraints.
For example, JP 2008-206231A proposes a method of detecting foreign metal according to the modulation rate (information on amplitude and phase changes) during communication between the transmitter and receiver, while JP 2001-275280A proposes a method of detecting foreign metal according to eddy current loss (foreign matter detection according to DC-DC efficiency).